1. Field of the Invention
The present invention relates generally to methods for guiding a catheter or needle to a preselected point within a patient's body, and more particularly, to a method for guiding biopsy needles, drainage catheters and the like, into a patient's body in conjunction with a C.T. scanner.
2. Description of the Prior Art
In recent years, total body C.T. scanners have become commonly used to provide doctors with a cross-sectional picture of a patient's internal organs and tissues. This imaging modality can define abnormal tissues but, in many situations, cannot determine what has caused the abnormality. Through the use of C.T. scanner technology, physicians are able to accurately place biopsy needles and drainage catheters into abnormal tissues with a high degree of success and with a low morbidity and mortality to the patient This approach has changed the way in which medical diagnoses are made. For example, exploratory laparotomies for suspected tumors have decreased significantly in recent years in view of the increasing use of C.T. guided biopsies of suspicious masses in the abdomen.
C.T. scanners that are presently available are capable of measuring a proposed trajectory for a biopsy needle or drainage catheter to within 0.1 millimeters with respect to depth, and within 0.1 degree with respect to angular orientation. However, there are no known methods available, apart from the method disclosed in applicant's U.S. Pat. No. 4,733,661, which can accurately and easily utilize such information to properly position a biopsy needle or drainage catheter relative to the patient's body. To the applicant's knowledge, most physicians perform C.T. guided procedures by initially positioning the needle or catheter at a rough estimation of the desired angle, and by then slowly advancing the needle or catheter into the patient's body, taking numerous C.T. scans along the way to determine the actual position of the needle or catheter, and altering its trajectory as needed. This trial and error technique has major disadvantages. First, it usually requires a relatively long period of time and causes the patient to remain in a fixed position which most patients find uncomfortable. Secondly, additional radiation may be harmful to the patient. Additionally, in institutions where C.T. access is limited, a lengthy procedure may excessively utilize the available time, preventing other patients from being studied.
C.T. scanner guided stereotactic brain surgery is known in the art, and various patents disclose frames for attachment to a patient's head for performing a stereotactic surgical procedure. Such stereotactic surgical apparatus for use in conjunction with C.T. scanners is disclosed in U.S. Pat. No. 4,341,220 and U.S. Pat. No. 4,592,352. The brain, because of its consistent relationship to the boney skull, can have a rigid frame attached to it which can then provide the needed reference coordinates from which various paths can be calculated. However, with respect to other parts of the body, underlying organs and tissues do not bear a constant relationship to the surface anatomy. In addition, parts of the body other than the head lack a sufficiently rigid structure to which a stereotactic frame can be reliably attached.
U.S. Pat. No. 4,058,114 to Soldner discloses a guide aide designed to introduce a puncturing cannula into the body under the guidance of ultrasound imaging equipment. The disclosed apparatus requires that the guide aide be secured to the ultrasound transducer. The disclosed apparatus further requires a targeting aide fastened to the ultrasound image viewing screen. The ultrasound transducer rests upon the patient's body and provides a support for the guide aide. In contrast, C.T. scanners do not utilize a transducer in contact with the patient's body, and accordingly, the guide aide and targeting aide disclosed by Soldner could not be used in conjunction with C.T. guided interventional procedures.
U.S. Pat. No 4,583,538 issued to Onik et al. discloses an apparatus designed to facilitate C.T. guided biopsies of the body. The stereotaxis guide instrument disclosed in this patent is floor-mounted and is designed to position a needle guide by moving the same through any of three perpendicular axes. Angular rotations about such axes are permitted to orient the needle guide in any desired direction. However, the articulated arm configuration disclosed by Onik et al. requires the user to manipulate a great number of cranks, bearings, and arms before a needle can be inserted into the patient.
The aforementioned patent to Onik further discloses a method for placing probes in a body based on images from a C.T. scanner. The method disclosed in the Onik patent consists of placing a localizer device made of carbon fiber on the patient's body to cause the localizer device to appear in the C.T. scanned image. The localizer device includes a base which must be aligned parallel to the C.T. scanning plane. A first scan is made through a first scan plane to locate a reference point on the scanned image corresponding to an edge of the localizer device in the scanned plane A skin entry point is also located on the scanned image and the distances between the reference point and the skin entry point along x and y axes are measured. A second scan is made through the target area in the patient's body. Coordinates for the positions of the skin entry point and target point, along the x, y, and z axes, are determined, and the azimuth, angle of declination, and needle path length are calculated. The Onik patent specification further states that the scan plane of the skin entry point and the scan plane of the target area may be in the same plane. While the above-described method disclosed by Onik is technically accurate, the use of the aforementioned localizer device, and the need to locate the same within a scanned image to generate a reference point, is believed to unnecessarily complicate such method.
C.T. scanners are adapted to project a laser-generated longitudinal reference beam along the central longitudinal axis of the scanning table. This longitudinal reference beam serves to designate, upon the patient's body, the vertical axis of all scanned images generated by the C.T. scanner. C.T. scanners are also adapted to project a first laser-generated transverse reference beam within the gantry of the scanner and perpendicular to the longitudinal reference beam to indicate the actual portion of the patient's body through which a scan is being taken. A second transverse reference beam is also projected by the C.T. scanner outside the gantry and parallel to the first transverse beam and spaced therefrom by a predetermined distance. Once a target area in the patient's body has been scanned, the scanning table can be moved along the longitudinal axis by the predetermined distance to cause the second transverse beam to illuminate the same portion of the patient's body that was previously illuminated by the first transverse beam before the scanning table was moved. Applicant has determined that the aforementioned longitudinal reference beam and transverse reference beams may be used to quickly and accurately guide a biopsy needle, drainage catheter, or the like, toward the target area without the need for a localizer device of the type described by Onik.
Accordingly, it is an object of the present invention to provide a guidance method which allows a physician or other user to perform a C.T. guided interventional procedure within a patient's body accurately, easily and more expeditiously than methods used in the past to perform such procedures.
It is another object of the present invention to provide such a guidance method which eliminates the need to make repeated C.T. scans in order to insure that the biopsy needle or drainage catheter is correctly aimed toward the target area.
It is a further object of the present invention to provide such a guidance method which permits the ready identification of an insertion site upon the patient's body without requiring the attachment of a localizer device to the patient's body and without requiring the scanning of such a localizer device.
It is a still further object of the present invention to provide such a guidance method wherein a physician or other user can easily and continuously maintain the catheter within the plane of the patient's body that was scanned by the C.T. scanner to locate the target area.
These and other objects of the present invention will become more apparent to those skilled in the art as the description thereof proceeds.